Cross contamination

[Pleco Fan]

So I'm new to keeping Discus and it seems its a steep learning curve, I came across "Cross Contamination" which Snow Patroll talks about.
Just how common is this when adding new Discus from a different source?
I have been keeping tropical fish on and off for three decades, but these fish whatever the challenges are worth the effort they are unlike any other fish I have ever kept.  [size=78%] [/size]

[TropicalFishForums]

[plankton]

You mean SnowAddict.
Yes, there is a theory that the different sources could have different problems and the different pathogens will cause a problem with new fish from elsewhere and vice versa.
There's also the theory about discus and angels carrying different pathogens, so it can be unwise to mix them.